Today I'm calling on all Londoners. Whatever else is on your to-do list this week, make sure that, on Thursday, you go out and vote.

I understand why European elections rarely enthral the public. But these matter. UKIP are throwing everything they have at this campaign. Your vote is the only way to stop them making gains.

Over the last few weeks, when I've been campaigning across London, delivering leaflets and knocking on doors, I've met people who say they're relaxed about UKIP winning seats. They are fed up with the other parties. Nigel Farage's party does at least, they say, offer a change.

But don't be fooled: its change of the worst kind. Behind the crowd-pleasing, pint-swilling banter is a party that wants to turn the clock back. UKIP's only answer to the complexities of the modern world - in which our lives and communities have been transformed with dizzying speed - is pulling up the drawbridge, shunning the outside world and hankering for some bygone past. These are people who resent the 21st Century.

Nothing could be more at odds with the values and attitude that make our capital great. This is the most open, diverse and cosmopolitan city on the planet, where people of every colour, creed and background live side by side. Outward-looking and forward-facing, London is at the vanguard of every major cultural and technological change. It's a city that embraces the future: boundless in its ambitions for what its industries and inhabitants can achieve.

London is, however, also home to much deprivation and hardship - and this is where UKIP see their chance. Their tactic is to play on the anxieties and insecurities that are rife in some of London's poorest boroughs. They offer easy solutions - not least on immigration and Europe, where they argue that all of our problems will magically disappear if only Britain unshackles our self from the continent, retreating back across the English Channel and locking the door behind us as we do. If UKIP win seats in the European Parliament this week, that is precisely the end they'll pursue.

But we live in a world where isolationism is masochism. Turning away from our neighbours would massively undermine Britain's interests, with London paying a particularly high price. European exit would hurt that vast numbers of businesses which sell their goods and services across the EU - our biggest export market - threatening livelihoods and jobs. It's also the surest way to pull the rug out from under the City. Right now the Square Mile is Europe's financial centre. Twice as many Euro foreign exchange deals happen in London than in any other country in the Eurozone. Holding this position in our own backyard is essential if we want our financial services to continue to compete with the best in the world. But if we leave the European Single Market this competitive edge disappears.

So vote. Vote to stop all of that. Polls open at 7am and close at 10pm. Chances are your polling station is spitting distance from your front door. Visit it before you take your children to school, on your lunch break, on your way home, after dinner - make the time however you can. Don't allow these people into a position where they can speak in your name. Act now, before it's too late.

You may not have voted for the Liberal Democrats before, but back us on Thursday to help us protect this city. We are the only party that has been prepared to take on UKIP. How many times you've heard David Cameron or Ed Miliband enter into this debate? None? That's because they won't. Labour and the Conservatives are too intimidated: scared that if they speak out against Farage it will cost them support. It has fallen, squarely, to the Liberal Democrats and it's a fight we relish - because UKIP are everything that we are not.

I lead a party of people who do not fear the future, but embrace it. Who do not regret diversity, but celebrate it. We are internationalists to our core because we understand that the biggest challenges Britain faces today are those which demand we work with others, whether it's preventing terrorism, tackling climate change, promoting free trade or clamping down on organised crime. We see that there is strength in numbers in an increasingly uncertain, fluid and interconnected world. We know that nations are stronger together than we are apart.

Above all, I lead a party that will always fight stop those who seek to sow division and exploit fear. That is precisely what UKIP do. The more we hear from Nigel Farage, the more we see his mask slipping. Despite all the criticism at the time, I feel it was right that I took him on in one-to-one debates because they have helped to lead to the scrutiny of his views which he has managed to escape for far too long.

However much Nigel Farage tries to disown the backwards and abhorrent views repeatedly espoused by the people he leads, his party holds an unmistakably regressive and ungenerous view of the world. Farage himself has said women are "worth less" to their employers because they go off and have children; he is hand-picking nationalities who he doesn't want to live next door to; he refuses to support gay marriage (one of my proudest achievements in government); he has said caring about climate change may be the biggest, stupidest mistake in history; he says Vladimir Putin is the politician he admires most.

These people must be stopped. The Liberal Democrats are doing everything we can but ultimately your vote is the thing that will make a difference. You can exercise your democratic right to prevent a party of populists and rabble rousers from gaining a foothold, and you can use your voice to stand up for the openness and tolerance that defines our capital. Whatever else you do this week, make a date with yourself: on Thursday go and vote.